Medical professionals use a variety of medical devices to measure a patient's vital signs during a routine checkup. Such devices can measure, for example, blood pressure, blood oxygen saturation (called O2 saturation), electro-cardiograms, heart rate, respiratory rate, and blood glucose level. A sphygmomanometer measures blood pressure with an inflatable cuff and sensing electronics that determine the patient's systolic and diastolic blood pressure. Another medical device, called a pulse oximeter, clips to the patient's finger and measures the percentage of haemoglobin that is saturated with oxygen. To make this measurement, the pulse oximeter includes separate light sources (e.g. diode lasers or light-emitting diodes) that emit radiation at two different wavelengths (typically 650 nm and 805 nm). Haemoglobin in the blood partly absorbs the light to a degree that depends on whether it is saturated or desaturated with oxygen. A calculator in the oximeter calculates the absorption at the two wavelengths and computes the proportion of haemoglobin that is oxygenated. The data are dependant on a pulsatile flow of blood and are typically plotted as a waveform that the calculator additionally analyzes to determine the patient's heart rate.
An electrocardiography measurement device measures a patient's electrocardiogram (ECG) with at least three conductive electrodes that attach to the patient. The electrodes detect time-dependent electrical impulses generated by the patient's beating heart. The measurement device also includes software that analyzes the impulses to determine a time-dependent waveform from which the patient's heart rate and cardiac response are calculated. The same electrodes used to measure an ECG can also include transducers or accelerometers that detect a patient's respiratory (i.e. breathing) rate.
Diabetic patients typically monitor their blood glucose level using a simple device called a glucometer. For these measurements, the patient draws a small sample of blood (by pricking a finger, for example) and applies this to a test strip. The patient then inserts the test strip into the glucometer, which includes an electrical system to determine the electrical properties of the blood. Software in the glucometer uses these properties to determine the patient's glucose level.
In typical applications, data indicating blood pressure, O2 saturation, ECG, heart rate, and respiratory rate are measured during a patient's appointment with a medical professional, such as a doctor, nurse, or certified diabetic educator. Once measured, the medical professional manually records these data in either a written or electronic file. Appointments typically take place a few times each year. And in some cases patients experience ‘white coat syndrome’ where anxiety during the appointment affects the vital signs that are measured. For example, white coat syndrome can elevate a patient's heart rate and blood pressure; this, in turn, can lead to an inaccurate diagnoses.
A diabetic patient will typically use a glucometer to measure their blood glucose levels several times each day, typically before and after meals. The patient may record the data in a logbook, which is then reviewed during at home or during a medical appointment. Some glucometers additionally include both electronic memory and a serial interface. In this case a personal computer equipped with the appropriate software and serial cable can download data from the glucometer and store it electronically in a file. The software may also include graphical capabilities that can, for example, plot data so that the patient can make a relatively sophisticated analysis of their blood glucose level.
Some medical devices for measuring the above-mentioned vital signs include systems for transmitting data from a remote site, such as the patient's home, to a central database. These systems can include a conventional computer modem that transmits data through a telephone line to the database. Or alternatively they can include a wireless transmitter, such as a cellular telephone or a radio modem, which wirelessly transmits the data through a wireless network.